The invention pertains to a heating arrangement for a moving material web or strip particularly a pre-heater for a corrugated cardboard facility having the a heating roll for transferring heat to the moving material web.
A heating arrangement for use in preheating a moving material web is known, for example, from DE 23 02 449 C3. Said arrangement consists of a heating roll which can be heated, preferably, by means of steam as a thermal medium. Heating of a material web occurs by means of the fact that said material web wraps around a heating roll at a predetermined looping angle. In order to be able to adjust the amount of thermal energy supplied, two guide rolls are provided in the known arrangement which can pivot about the outer periphery of the heating roll. Said guide rolls feature a fixed relative position to each other and, for said purpose, are arranged on two arms connected to each other in a rigid connection. Said arms can pivot together about the axis of a heating roll by means of a suitable driver.
In a position defining the minimum looping angle, both guide rolls are positioned out of contact with the material web. Said material web, which is supplied by means of a fixed guide roll on the inlet side, passes around the heating roll in this position at a certain remaining looping angle to a fixed guide roll on the outlet side.
Both pivotable guide rolls can pivot, in the direction of the circumference, away from said position until the front guide roll in the pivoting direction comes into contact with the material web. If the two guide mechanisms are pivoted further, the looping angle increases accordingly. In order to avoid dragging the web section between the fixed guide roll on the inlet side and the roll defining the looping angle, said web section, after a certain pivoting angle has been exceeded (calculated from the position of the minimum looping angle) is held, together with the second pivotable guide roll, at a sufficient clearance from the heating roll.
This known heating arrangement enables a maximum looping angle. In addition, this embodiment ensures, at the position of the minimum looping angle (remaining looping angle), an extremely simple feed of a material web to be heated. This is because the material web need only be guided between the peripheral surface of the heating roll and the two pivotable guide rolls.
Nonetheless, a disadvantage of said heating arrangement is that there is a certain remaining looping angle and as a result, a definite minimum amount of thermal energy is unavoidably applied to the material web.
In addition, an arrangement for preparing a material in web form, such as corrugated cardboard for gluing, is known from DE-OS 15 11 061, for which a material web likewise is guided about a pivotable guide roll. In the position resulting in a minimum looping angle with the use of one individual guide roll, an additional guide roll moves into engagement, in said known arrangement, which in this position lifts the material web completely from the surface of the periphery of the heating roll. In said position with a zero looping angle, the material web forms an S shape between the two guide rolls. Again, the guide roll which lifts the material web at the position having a zero looping angle is in fixed connection with the guide roll defining the looping angle. Both guide rolls can pivot about the axis of the heating roll by means of a pivoting arm. Consequently, this arrangement allows the application of energy to the material web to be eliminated completely in the position of zero looping angle.
However, a disadvantage of said known arrangement is that only a relatively limited maximum looping angle may be achieved. With this known embodiment, increasing the diameter of the heating roll is the only way to achieve an increase in the heated length. This is accompanied by considerable cost.
Starting from this state of the art, the underlying purpose of the invention is to create a heating arrangement for a moving material web, particularly a pre-heater for a corrugated cardboard facility, for which a maximum heated length of said material web is achieved at the least possible expense and for which at the same time, the heated length can be adjusted to zero in a simple way.
Providing a third guide mechanism according to the invention, which of course, can also be in the form of a guide roll, for a heating arrangement according to DE 23 02 449 C3, achieves both the advantages of providing a maximum looping angle (and consequently a maximum heatable length of a material web) and also of varying the looping angle or the heatable length to zero.
According to the preferred embodiment of the invention, all guide mechanisms are connected to a carrier which can pivot about the axis of a heating roll. In this connection, all guide mechanisms can feature the same clearance from the periphery of the heating roll.
In the preferred embodiment of the invention, the third guide mechanism, which lifts a material web at the position of zero looping angle, is arranged at a minimum permissible clearance from the first guide mechanism in the direction of the circumference of the heating roll. This provides the advantage of a maximum looping angle since the three guide mechanisms which pivot together can pivot by the maximum possible angle before the third guide mechanism comes into contact with the entering or exiting section of the material web. Of course, the third guide mechanism must be arranged in the radial direction (with respect to the heating roll), such that in the position of zero looping angle, a lifting of the material web from the peripheral surface of the heating roll actually occurs.
According to the preferred embodiment of the invention, a material web is supplied by means of a fixed guide mechanism on the inlet side and carried off by means of a fixed guide mechanism on the outlet side, wherein the guide mechanisms on the inlet side and outlet side are located, in essence, on a straight line with the axis of the heating roll. This provides the advantage of the maximum possible looping angle. This is approximately 270-280xc2x0.
According to one embodiment of the invention, the third guide mechanism may, with respect to the heating roll, be offset in an outward radial direction in comparison with the first guide mechanism. In this connection a material web wraps around the first and third guide mechanism in an S shape in the position of the minimum looping angle (zero looping angle).
If in said embodiment, the third guide mechanism is arranged within the mid-point angle defined by means of the axes of the first and second guide mechanisms and the axis of the heating roll, then the guide mechanisms can pivot until the first guide mechanism barely does not come into contact with the section of the material web on the inlet side or outlet side. This provides the maximum looping angle.
In this embodiment, in the position of zero looping angle, the material web wraps around the first and third guide mechanisms in an extreme S shape. Again, this makes threading a material web more difficult, for example, after a tear. For this reason, a third guide mechanism can be transported from the normal working position into a threading position in front of the first guide mechanism in the direction of the circumference of the heating roll. This may occur, for example, by means of pivoting the third guide mechanism about the axis of the first guide mechanism. In this connection, it may be preferable to develop a third guide mechanism that can be locked in the threading position and/or working position.